An Analysis of the Roles of Stress, Temperature, and pH in Chemical Compaction of Sandstones: Discussion

Abstract

In a recent article on chemical compaction of sandstones, Sheldon et al. (2003) claim that models of quartz cementation based upon the diffusional transport of dissolved silica originating from the clay-induced dissolution (CID) of quartz at stylolites are untenable because no chemical driving force is available to drive silica diffusion in the aqueous phase. As examples of such untenable models, they cite a number of our papers (Oelkers et al. 1992, 1996; Walderhaug 1994; Bjorkum 1996; Bjorkum and Nadeau 1998; Bjorkum et al. 1998; Walderhaug et al. 2001). In the following discussion of their paper we will demonstrate that there is indeed a driving force for aqueous silica diffusion within the CID quartz cementation model and point out several flaws in the Sheldon et al. (2003) treatment of quartz dissolution at stylolites. Contrary to the claims of Sheldon et al. (2003), the quantitative models of quartz cementation presented in Oelkers et al. (1992, 1996), Walderhaug (1994, 1996), and Bjorkum et al. (1998) do not claim to present, nor do they depend upon, a detailed understanding of the mechanisms of quartz dissolution at stylolites. These models are based upon an overwhelming number of petrographic observations indicating that (1) quartz dissolution in quartzose sandstones occurs predominately at quartz-clay and quartz-mica interfaces (clay-induced dissolution; CID) and (2) this enhanced quartz dissolution requires negligible stress (see Bjorkum 1996). The actual mechanism which increases quartz solubility at these interfaces is unclear; it may result from an electrostatic interaction between quartz and clay mineral/mica surfaces, but this has yet to be demonstrated unambiguously. Nevertheless, just as Newton's law of gravitation enables useful calculations without providing insight into the underlying causes of gravity, these quartz cementation models provide accurate predictions of quartz cement volumes in quartzose …